United States Application Ser. No. 82,150, now U.S. Pat. No. 3,285,730, filed Oct. 5, 1979 in the names of L. M. Sanford and P. A. Tick, discloses a group of glasses having compositions within the alkali metal oxide-alkaline earth metal oxide-fluoride-phosphate field (R.sub.2 O-RO-F-P.sub.2 O.sub.5) displaying low transition temperatures (T.sub.g) and the capability for molding and otherwise shaping glass bodies under pressure at low temperatures, viz., below 450.degree. C., without the need for hydration. Those glasses have base compositions consisting essentially, expressed in mole percent on the oxide basis as calculated from the batch, of about 15-45% R.sub.2 O, consisting of 0-45% Li.sub.2 O, 0-20% Na.sub.2 O, and 0-10% K.sub.2 O, 0-20% RO, consisting of 0-10% MgO, 0-15% CaO, 0-20% SrO, and 0-20% BaO, 25-55% P.sub.2 O.sub.5, with 0.3-3% by weight F, as analyzed in the final glass. Optional constituents therefor include up to 20% PbO, up to 7% La.sub.2 O.sub.3, and up to 12% ZnO. The essential absence of Al.sub.2 O.sub.3 is stated to be much preferred. Where the P.sub.2 O.sub.5 content is less than 30%, B.sub.2 O.sub.3 may be incorporated in amounts up to 25%. Where the content of P.sub.2 O.sub.5 is at least 45%, B.sub.2 O.sub.3 will be present at levels no greater than 5%. The sum of all optional ingredients other than RO and R.sub.2 O will not exceed 25% and the total of all optional components exclusive of RO will be less than 35%.
It is explained in that application that vitreous, phosphate-based compositions containing fluoride are well known to the glass art but that such are commonly plagued by two seemingly intrinsic undesirable characteristics, viz., relatively poor chemical durability and a tendency to devitrify during forming and working. Many glasses also demonstrated poor resistance to weathering, i.e., they were attacked upon exposure to the ambient environment.